The primary object of the present invention is to provide a slow start valve. The valve is intended for use in hydraulic and other fluid-type systems.
The present design is intended to provide a gradual increase in hydraulic flow (and thus hydraulic pressure) upon activation of the pump or other motive means for the hydraulic device in such a manner that the hydraulic fluid does not surge through the system and "hammer" the apparatus.
Although the valve art is relatively highly developed, there is no prior design of which I am aware which accomplishes the slow start function of the present device.
For example, Brooks U.S. Pat. No. 3,604,446 is a fluid valve for a gas turbine engine. The valve does not open until a minimum inlet pressure is reached. At that time, the output valve opens abruptly, so that there is no gradual increase in pressure at the output end of the device. By contrast, the present invention produces such a gradual increase in pressure at the output end of the device. Moreover, Brooks is intended to be operated at a constant pressure, a limitation which the present device is not under.
Another patent which exemplifies the prior art is Slomer U.S. Pat. No. 2,649,688 entitled "Feed Control for Hydraulic Motors". As in the case of the present invention, the Slomer device has as it objective the prevention of so-called hydraulic hammer and the provision of means for the smooth application of hydraulic pressure fluid to hydraulic motors or cylinders. However, the Slomer Patent discloses a hydraulic motor control valve means which in fact is useful only in connection with a main control valve mechanism which is operated by a control handle. In addition, the hydraulic motor feed control of Slomer involves at least three interior valves. As will be seen, the present invention is a much simpler design and accomplishes an improved function compared to the Slomer Patent.
A similarly complicated device shown in Oyster U.S. Pat. No. 2,905,190 for "Hydraulic Shock Damping Apparatus". As in the case of Slomer, the device, which the patentee calls a "pressure responsive control valve" is in fact utilized as an auxillary mechanism in connection with a manually operated open center valve, and is a hybrid mechanism designed for the purpose of reducing hydraulic shock and also to operate as a relief valve. Essentially, this is a shunt type device which, like Slomer, operates only upon an increase in pressure. By contrast, as will be observed from the following description, the present invention has only one moving element and acts upon oil flow alone independent of system pressure.
U.S. Pat. No. 2,609,829 to Davies for "Emergency By-Pass Valve for Fluid Circuits" is an emergency by-pass valve designed for airplane oil systems to return oil to the sump in case of a line rupture. This device requires that the return flow be equal to the input flow in order to operate. By contrast, the slow start device of the present invention does not require return flow for operation.
Chichester U.S. Pat. No. 3,455,322 for "Pressure Compensated Diverter Valve" discloses a relief type valve which does not operate to start movement of a piston gradually. The Chichester device dumps a portion of the input fluid to a relief passage when the pressure in the output passage reaches a certain level and is thus pressure sensitive. The slow start device of the present invention is essentially insensitive to system pressure and operates in response to oil flow and the attendant pressure drop across a single piston.
An older prior art device which illustrates the state of the art is Hipple U.S. Pat. No. 2,888,943 for "Control Valve Having Constant Volume Output Features". This device is manually operated to provide gradual starting of the motor system. The slow start device of the present invention, by contrast, is automatic in its operation.
Gartner U.S. Pat. No. 2,989,975 is a regulator type valve device for maintaining constant pressure drop between upstream and downstream sides of liquid flow under varying rates of flow. The valve dumps or bypasses more fluid with increased system pressure. Bypassing a fluid continues when the pressure is maintained constant. In the slow start device of the present invention, bypassing occurs only as flow is initiated and is a transient effect. Thus, under steady-state conditions, no fluid (or an inconsequential amount) is bypassed. In addition, the action of the slow start device of this invention is essentially the same over wide variations in the system pressure.
The foregoing descriptions of the illustrative prior art indicate some of the differences between the present invention and the prior art. Additional differences will be understood from a reading of the following detailed description of one preferred embodiment of the present invention, and from the drawing.